A fractionator is a machine that utilizes the ultra-filtration or reverse osmosis technique of membrane separation for food products and by-products.
One typical use for the machine of the present invention is to separate the protein out of cheese whey, as disclosed in U.S. Pat. No. 3,880,755, although it is not restricted to this use. The embodiment disclosed in the present invention utilizes a spiral wound element which consists of a sealed envelope of membrane material resembling a plastic bag, the neck of which is attached to a hollow tube, the latter having a series of holes running longitudinally. These holes communicate with the neck of the bag so that material that passes through the membrane will migrate to the neck of the bag, enter the hollow tube through the holes therein, and be drawn off. The plastic-like bag is wound up in a spiral manner much like a window shade, and the entire outside is covered with a wrapping. These elements or modules are then placed end to end in long tubes, usually six to a tube, and conncted together with special interconnectors as shown in U.S. Pat. No. 3,880,755. U.S. Pat. Nos. 3,367,504 and 3,933,646 also disclose spirally wound membrane envelopes.
In this general type of apparatus there is an annular space between the outer surface of the module and the inner surface of the tube in which product might flow and bypass the module. To prevent this, U.S. Pat. No. 3,880,755 discloses a one directional lip-type seal attached to the outside of the module so that, in forward flow, the product is forced to flow through the module.
In water purification systems, the above described arrangement is very desirable, but in food product applications, and in particular where the food is intended for human consumption, the lip seal has presented a serious problem. The modules are customarily 39 inches long, and the lip seal is close to the leading edge. Thus the product can then get back to the seal from the backside and become stagnant. To prevent this, health authorities have required that the machine be stopped every 30 minutes, that the valves be adjusted, and that the pumps be restarted so that flow is established in the reverse direction for one minute. The purpose of this is to force the stagnant product past the lip seal by collapsing it and, thereby, replacing it with fresh product. This method was acceptable but required complex programming of switches, required extra controls, and caused undue wear and tear on the modules, and lost production time.